The central aim of this proposal is to dissect the molecular mechanisms leading to tissue injury, and organ dysfunction in severe hemorrhagic shock (HS). Visualization and localization of message, protein, or structural changes leading to, or resulting from each step in this dynamic process is essential in understanding the molecular mechanisms of HS. The different projects within this proposal focus on defined tissue systems including gut, liver and lung within either a rat or mouse model of HS. In each case a wide range of microscopic methods will be employed and are considered essential in gaining an understanding the pathology of HS at the tissue and cellular level, thus a central cell and tissue imaging core is defined as an integral component of this proposal. The Core will be housed in the Structural Biology Imaging Center (SBIC) of the University of Pittsburgh Medical Center. This Center is equipped to perform a continuum of optical methods including all types of microscopy essential to this Program Project. Within the scope of this Program light microscopic techniques include: histological, immuno-histological, laser confocal, and in situ hybridization technologies. Our considerable experience in computerized image processing and morphometry will allow quantitative analysis of observed phenomena to corroborate subtle qualitative changes, and this a major function of the Core in this Program. At the electron microscopic level thin section electron microscopy and immuno-electron microscopic evaluation of specimens as a natural extension of the light microscopic analyses will be employed when needed. The SBIC currently collaborates extensively with several of the Project Leaders involved in this Program and we expect a substantial increase in the use of optical techniques within the formal setting of this Program.